1) Technical field of the Invention
The present invention relates to a semiconductor element used for a contact-type semiconductor device such as a gate turn-on thyristor (GTO thyristor) and a gate commutated turn-off thyristor (GCT thyristor).
2) Description of Related Arts
Recent gate turn-on thyristors have widely been utilized as key devices of power electronics equiptments for controlling substantial current running across high potentials. Such power electronics equiptments includes, for example, a SVG (Static Var Generator), a BTB (Back To Back) system, and an inerter circuitry for driving motors of an iron-making roller.
Although not illustrated herein, the gate turn-off thyristor has a multi-layer structure of four p-n-p-n layers, which includes an n-type uppermost emitter layer (NE layer) that is etched to have a plurality of island regions, and a plurality of cathode electrodes on the island regions of the emitter layer. Also, the gate turn-off thyristor includes a p-type base layer (PB layer) beneath the uppermost layer, a gate electrode on the PB layer surrounding the island regions of the emitter layer, and an anode electrode formed on a lowermost p-type emitter layer (PE layer).
In a normal operation of the gate turn-off thyristor, it is turned on by forward pulse current running through the gate electrode while the voltage is applied between the anode and cathode electrodes, and after turning on, it can be turned off by reverse current running across the gate and cathode electrodes (self turn-off feature).
Various gate turn-off thyristors have been proposed in many references, for example, as listed below.
Japanese Patent Application JP 62-136875, A
Japanese Patent Application JP 55-136875, A
Japanese Patent Application JP 63-173363, A
However, once a small amount of leak current may run, with some reasons, between the cathode electrode and the gate electrode that are arranged close to each other, the turning-off timing (switching-off point) is delayed, and also greater amount of the gate trigger current is required for turning on the thyristor. This inhibits reliable switching operation of the gate turn-off thyristor as designed.
Therefore, the present invention is to address the drawbacks and to provide a semiconductor element minimizing the leak current between the cathode electrode and the gate electrode thereof for realizing highly reliable switching operation of the semiconductor element.